Base Curves

**chip anderson** · 07-02-2006, 02:20 PM

Just something to kick around. As the "base curve" is now the front surface, shouldn't vertex distances now be measured from the anterior of the lens to the anterior of the cornea?

Should one calculate the anticipated thickness of the lens and the amount of protrusion from the frame-to-be dispensed for real accuracy?

Chip

An no I'm not smart enough to do this even after Daryll tells us how.

**HarryChiling** · 07-02-2006, 02:37 PM

I wouldn't think so considering we make changes to the back vertex power of the lens, which is measured from the posterior of the lens.

**Jim Stone** · 07-02-2006, 04:09 PM

Originally Posted by chip anderson

Just something to kick around. As the "base curve" is now the front surface, shouldn't vertex distances now be measured from the anterior of the lens to the anterior of the cornea?

Should one calculate the anticipated thickness of the lens and the amount of protrusion from the frame-to-be dispensed for real accuracy?

Chip

An no I'm not smart enough to do this even after Daryll tells us how.

Why bring this up. You go to school where they taught the base curve was the flattest curve. Some freaking bubble head! The base curve is the front surface.

**chip anderson** · 07-02-2006, 05:14 PM

Jim Stone:

When I went to school the base curve was the posterior Surface whether the flattest or steepest. It's only you young whippersnappers that weren't learned no better.

**Jim Stone** · 07-02-2006, 07:57 PM

Originally Posted by chip anderson

Jim Stone:

When I went to school the base curve was the posterior Surface whether the flattest or steepest. It's only you young whippersnappers that weren't learned no better.

Posterior means back. Us whippersnapers been refering to the base curve as the finished side of the lenses we were taking out of the boxes. It aint the back. Simple enough for you chip? The old guys were doing that when this whippersnapper in Jan . of 1973. Some optical books refer to the base curve as the lowest curve anywhere. PFS! Pretty simple!

**chip anderson** · 07-02-2006, 08:18 PM

This whipper snapper started in the business in '58, started working from Virgil Hancock at Modern Optics. Of course I admit that most of my experience has been contact lenses and the base was always the back until B&L brought out it's C series of contacts and muddled the water.

**Jim Stone** · 07-02-2006, 08:25 PM

Originally Posted by chip anderson

This whipper snapper started in the business in '58, started working from Virgil Hancock at Modern Optics. Of course I admit that most of my experience has been contact lenses and the base was always the back until B&L brought out it's C series of contacts and muddled the water.

OH! Contacts. I see now. Sorry!

**HarryChiling** · 07-02-2006, 10:58 PM

Originally Posted by Jim Stone

Us whippersnapers been refering to the base curve as the finished side of the lenses we were taking out of the boxes.

On the back curve or surfaced side of the lens the two curves are referenced as the base and cross curves.

**Chris Ryser** · 07-03-2006, 02:51 AM

When I had my wholesale lab..............for a period of 20 years which included the plastic lens area towards the end.

When ordering lenses mostly from AO at the time we got the lens blanks with specified finished curves which were the front surfaces and then surfaced the back side. This is still the case today............... base curve is on the front.

**Jim Stone** · 07-03-2006, 07:15 AM

Originally Posted by HarryChiling

On the back curve or surfaced side of the lens the two curves are referenced as the base and cross curves.

Heck yea Harry. I forgot about that. As generators cut!

**Jim Stone** · 07-03-2006, 07:19 AM

Originally Posted by chip anderson

Just something to kick around. As the "base curve" is now the front surface, shouldn't vertex distances now be measured from the anterior of the lens to the anterior of the cornea?

Should one calculate the anticipated thickness of the lens and the amount of protrusion from the frame-to-be dispensed for real accuracy?

Chip

An no I'm not smart enough to do this even after Daryll tells us how.

Back to this. You'd have to use the what the whippersnappers around here call the sag formular. Get the thickness. Then figure the vertex change, get the thickness again. Then figure the vertex change, get the thickness again. Then figure the vertex change, get the thickness again. Then figure the vertex change, get the thickness again. Seems I am looping! Stick to the back, please.

**William Walker** · 07-03-2006, 10:10 AM

I would think we'd still want to refer to the vertex as the posterior side of a spec lens, since any phoropter vertex reading would be to the posterior side of the trial lens.